Computational Modeling of Joist-to-Ledger Connections in Cold-Formed Steel Diaphragms

Abstract

Cold-formed steel framed buildings can involve a range of options for framing systems, including balloon framing, platform framing, and ledger framing. Transfer of lateral forces from the diaphragms to the wall system (and ultimately to the ground) depends on the interactions within the wall-diaphragm connection, which is dependent on choice of framing system. In ledger framing, floor joists are hung from top of wall studs via a rim track (ledger) and clip angle connection. Recent experimental efforts at Johns Hopkins University studied the wall-diaphragm connection with the goal of quantifying its contribution to overall diaphragm response. Results from these experiments showed the contribution to the rotational stiffness based on the location relative of floor joist and wall stud, location of clip angle, presence of top/bottom screws at ledger/joist flanges and presence of oriented strand board (OSB). In addition, it was observed that ledger flange buckling, and wall stud web crippling were the primary limit states. In current design codes there is not check for these limit states. The objective of this paper is to provide a robust computational model for a joist-to-ledger connection in CFS floor diaphragm with the ultimate goal of expanding the experimental test variables via a parametric study the computational model is compared and validated with experimental results. This detailed work at the connection level will motivate and inform future efforts for complete diaphragm system modeling. Furthermore, the work herein will lead to more robust modeling and prediction capabilities for CFS diaphragms